;;; adjoin.lisp
;;;
;;; Copyright (C) 2003 Peter Graves
;;; $Id: adjoin.lisp 11695 2009-03-03 22:10:25Z ehuelsmann $
;;;
;;; This program is free software; you can redistribute it and/or
;;; modify it under the terms of the GNU General Public License
;;; as published by the Free Software Foundation; either version 2
;;; of the License, or (at your option) any later version.
;;;
;;; This program is distributed in the hope that it will be useful,
;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;;; GNU General Public License for more details.
;;;
;;; You should have received a copy of the GNU General Public License
;;; along with this program; if not, write to the Free Software
;;; Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
;;;
;;; As a special exception, the copyright holders of this library give you
;;; permission to link this library with independent modules to produce an
;;; executable, regardless of the license terms of these independent
;;; modules, and to copy and distribute the resulting executable under
;;; terms of your choice, provided that you also meet, for each linked
;;; independent module, the terms and conditions of the license of that
;;; module.  An independent module is a module which is not derived from
;;; or based on this library.  If you modify this library, you may extend
;;; this exception to your version of the library, but you are not
;;; obligated to do so.  If you do not wish to do so, delete this
;;; exception statement from your version.

(defun adjoin (item list &key key (test #'eql testp) (test-not nil notp))
  "Add `item' to `list' unless it is already a member (as determined by
the test function `test'."
  (when (and testp notp)
    (error "test and test-not both supplied"))
  (if (let ((key-val (sys::apply-key key item)))
	(if notp
	    (member key-val list :test-not test-not :key key)
	    (member key-val list :test test :key key)))
      list
      (cons item list)))
